Spark plug



March 1, 1960 A. cANDELlsE SPARK PLUG Filed Oct. 6, 1958 ad f y@ w .1\ y f I |I. ll l I? .l/ f M/ f WM n. HNF,

United States Patent O SPARK PLUG Alfred Candelise, Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Dela- Ware Application October 6, 1958, Serial No. 765,613

6 Claims. (Cl. 313`145) This invention relates to spark plugs and, more particularly, to an improved aircraft spark plug of the type having a cast silver centerwire section and platinum wire electrodes such as shown, for example, by United States Patents 2,162,062, issued June 13, 1939, and 2,400,917, issued May 28, 1946, to Douglas Haynes Corbin.

Spark plugs of the type covered by the aforementioned patents, i.e., having the cast silver centerwire section and platinum wire electrodes, are superior to any other presently known type of spark plug for use in extremely high output piston type aircraft engines. However, one diiculty which has been encountered with such plugs is that after prolonged periods of operation they tend to develop slight insulator cracks which originate adjacent the ring tip within the insulator centerbore and gradually work radially outwardly. Actually within the normal useful life of the present plugs of this type, as determined by the life of the electrodes, these slight cracks are generally harmless. However, sBch cracks do present a potential hazard in that a completely cracked insulator tip falling free of the spark plug could cause extensive damage to other components of the aircraft engine. Therefore, the occurrence of these minute cracks in the insulator tip has presented a problem standing in the way of the development of aircraft plugs having longer useful and reliable life.

The present invention has as one of its objects the provision of an aircraft spark plug of the aforementioned type having highly increased durability and reliability. Another object is the provision of an aircraft spark plug having a longer useful electrode life. More specifically, it is an object of the present invention to provide an aircraft spark plug of the type having a cast silver centerwire section and platinum electrodes, which has increased resistance to insulator failure and a longer useful life.

Other objects and advantages of the invention will appear more clearly from the following description of a preferred embodiment and from the accompanying drawings in which:

Figure 1 is a side view in partial section of a spark plug constructed in accordance with the invention;

Figure 2 is a sectional view of the bottom of a spark plug shown in Figure 1 but in larger scale; and

Figure 3 is a bottom view of the spark plug shown in Figure 1.

Referring now to Figure l, the spark plug Shown comprises a metal shell 4 having a metal shielding barrel 6 secured thereto, a ceramic insulator 8 secured concentrically within the shell-shielding barrel assembly, a centerwire assembly 10 within the centerbore of the insulator the lower and external portion of which serves as the center electrode, and a pair of platinum ground elecis that it provides additional tiring tip area and thereby 2,927,238 Patented Mar. 1, 1960 trodes -12 and 14 each having its outer end welded to the bottom of the shell 4 and its inner end in spaced relation to the center electrode to form a spark gap therewith. TheA precise structure of the metal shell-shielding barrel assembly and of the means whereby the insulator 8 is secured within this assembly forms no part of the present invention and is the same as that covered by United States patent application Serial No. 404,878, filed in the names of Wilfred A. Bychinsky and Alfred Candelise on January 19, 1954 and which is now United States Patent 2,874,323 issued February 17, 1959.

l,The centerbore of the insulator is formed with a lower section 16 of small diameter and an upper enlarged section 18, the junction between the two sections constituting a shoulder 20. The lower centerbore section tapers very gradually toward the tiring tip of the plug, i.e., without any abrupt changes in diameter or internal flange at the tip thereof such as in the plug shown by the aforesaid United States Patent 2,400,917. Likewise, the external surface of the insulator firing tip tapers gradually toward the bottom end thereof. vrI'hus, there are. no abrupt changes in the thickness of the insulator at the lower or firing tip end thereof.

Further in accordance with the invention, the bottom portion of the centerwire comprises a spindle having a cylindrical ring tip 22, a flange 24 (see Figure 2) abutting the tip of the insulator, a cylindrical portion Z6 fitting snugly within the lower end of the insluator centerbore and a shank portion 28 of reduced diameter which extends upwardly through the lower section of the centerbore and terminates with a thin curved hook the free end of which contacts the internal shoulder 20 of the insulator. If desired, the firing tip 22 instead of being cylindrical may be formed with fiat side surfaces oriented thereby increase the spark gap area of the firing tip. The

entire spindle may be of platinum or, if desired, the upper end may be of a less expensive heat-resistant metal, preferably a nickel wire secured as by welding to the platinum firing tip portion as shown at 30. Surrounding the entire shank portion of the spindle is a body of silver 32,' preferably centrifugally cast in situ as described in the aforementioned United States Patent 2,400,917.

The distance between the flange 24 and the platinum ground electrodes 12 and 14 is the same as that between the respective ground electrodes and the cylindrical tip 22. Thus, one of the important functions of the ange which has been conducted in conjunction with this invention, there is reason to believe that corrosion of the silver.

body has a direct bearing on the problem of insulator tip cracks. If desired, additional sealing may be provided l'by an annular body of cement 34 between the ange and the tip of the insulator as shown in. Figure 2.

A conductive glass seal 36 of a mixture of glass and nickel or copper powder abuts the upper surface of the cast silver body 32, a durable electrical connection between the silver and glass seal being formed by spiral' wire 38, the lower end of which is embedded in the silver.

The glass seal may be as disclosed in United States Patent 2,248,415, issued July 8, 1941 to Karl Schwartzwalder and A. S. Rulka.

`The centerwire of the embodiment shown hasV as one of its elements a resistor cartridge 40, the upper end Vof which is connected to a suitable contact (not shown) which serves as the means for making electrical connecinsulator slfioul'c'ler` 20, the'snug'ly fitting cylindrical por- Y n tion- 26'incombination with the upper bent portion maintaining thespindle centralizedV withinV the insulator centerbore." If it is desiredto provide additionalvr sealing, a

small amount of cementl may be placed over the tip of the insulator or over the/upper surface of the flange'24 just prior to `inserting the spindlegrthe assembly then be- Y ing` heated; if' required, tocure the cement. A;cerne'nt which is suitable forsuch sealing, is that covered byV United States Patent 2,829,0'615,l issuedApn'l l; 1958i tol Karlschwartzwald'er and'Arthur Vj Somers. l,

After the platinum-tipped electrode' spindle is firmly secured withintlie'insulator as described, a mass of silver is placediin the insulatory centerbore from thetop thereof,

. melted by heating and then cast, preferably centrifugally,

4 bore, at least the flange and ringtip portions `of said metal spindle being of platinum.

2. A spark plug comprising a generally tubular metal shell having at least one platinum ground electrode wire secured to the lower end thereof, an elongated insulator having a centerbore therethrough and secured concentrically Within said shell, said centerbore having a lower portion of reduced diameter and the wall thickness of said insulator diminishing gradually at the lower end thereof adjacent the ground. electrode, a metal center electrode spindle having a lower tiring tip portion spaced in spark gap relation tojsaid ground electrode, a ange to thereby-form the dense silver body 32. Prior to hardening'of'tl'ieV silver, the spiral wire is positioned, as shown,

such that'Y its bottomi portion becomes embedded in theV ilver.v To' form, the conductive glass seal, a charge of' metal-andV glass" inlpowder'form is placed in the centerbore and the assembly heatedto therebyfusejthe glass, pressure being "siz'nultaneouslyV applied so that a good bondlforms' between the glass mixture and the insulator.

portion having its upper surface in sealed relationship to thelower end of said'insulator and its lower surface spaced inV spark gap relation to saidgroundelectrode, a cylindrical portion fitted snugly within the lower end of the insulator centerbore and ashank portion` extending upwardly into said centerbore andV embedded in a body of silver within the lower'portion of said centerbore, at least the flange and firing Vtip portions of said metal spindle being` of platinum. Y

3.- A spark plugassetforthLinclaim 2 and including an=annular body of sealing. cement between said spindle andtthe ylower end of the insulator.

4. A sparky plug comprising a generallyV tubular metal shell'having at` least'one'platinum ground electrode wire Vsecured tothe lower end thereof, an elongated insulator havingla centerbore therethrough and secured concentricallyv withinLsaidv shell, said centerbore having a lower portion of, reduced diameter andthe wail thickness of said insulator diminishing. gradually atfthe lowerrpend Y, thereof adjacent the ground "electrode,v a metal` center Theresistor cartridge being-'positioned'asshown, alsuit-Y Y able electricalV Contact (not shown)4 is then, secured in placey in the conventionalmanner. VThe remainder of the assembly operations may beV asV described in Vthe aforesaid `United States Vpatent application Serial No.

V4045878; As a iinaloperation, the platinum groundrelectrodes 12- and 14"' may be adjusted by bending as requiredtoV provide the desired. spark gap. t

By farthe mostimportant advantage of the cornbina-V c tion of structural features shown' is that it provides@- highlyY improved resistance ltojinsulator failure. More specifically, ithasV been found [thatthe centerwire-insulatorA assembly''structure` provides optimum plug life and eration: This feature, in' addition to the longerY useful electrode life',V provides a greatly improved sparkVV plug having optimunrdurabilityand reliability.V v l v While the; invention has been` described' specifically Y withl reference to` a particular embodiment thereof,it is understoodthat vchanges andrnodifications may be made, Y all `within1the full and: intended' scopeof the claims whichV foupw.

Whatjis claimed is: V1'.V A 'spark plugv comprising a generally tubular metal 'shellh'a'ving at least one platinum .ground electrode wire-` secured `to Vthe. lower: end thereof; anl elongated insulator hav" portionof reduced diametenandjthe Wall thicknessrof portionabutt'ingrthelower-fend of'said insulator and" also spacedinf sparkingap? relationeto said ground; electrode, a cylindrical-portion fitted snugly-within theflowerend of the-'insulator'centerbore-andfa shank portion extend- Amg@upwardly-into `said cente'rbore and embedded in aV body Aof ksilver within the lower portion of,1 said ycenter- 'v glia.v ,centerboreirr therethrough and secured concen Vtrieally within said sheiL,saidi-centerbore having a lower V'durability-withfreeddnr from the slight insulator cracks whichhave heretofore developed adjacentV the firing.V tip of castsilver' center-wire type plugs after prolonged op` electrode spindle havinga lower tiring tip'portion spaced inV spark-gap: relation'to saidl ground electrode, a flange portion in sealed. relationship with the lower endlof said insulator and also spaced in spark gap relation toY said ground electrode, Va cylindrical portionl fitted snugly withinthe lower endof the insulator centerborel and a shank portion; extending4 upwardly into said centerbore terminating-with an-upper endportion in Contact. with said insulatoiysaid.v shankf portion being embedded in a body of silver within the'- lower portion of said centerbore, at

leastfthe angeandL-iing'ftipiportions of Vsaid metal spindle-being of;platinun1.` n Y 5.YV A sparkplug-.comprising agenerally tubular metal shell havingcat leastfoneV platinum; grol'lnd-electrodewire Vsecured tothe lower end thereof, an elongated insulator rhavingfacenterbore therethrough 'andY secured-concentrically Withinfsaid'shell, said-'centerbore having a lower portion of: reduced-.diameter and the wall? ,thicknessY of Ysaid insulator diminishing gradually' at4 theflower end thereofl adjacentr the ground. electrode, a metal lcenter electrode spindleV havinga lower iringptip portion V'spaced in spark gap relation to said ground electrode, a flange portionabutting the'lower end Vofisaid insulator and also space l'-v in` spark. gaprelation to` 'said ground; electrode,

i a cylindrical portionltted snugly` withidthe lower4 end of the insulator-,centerbore anda shankfportion extend-` I ing upwardly into said centerbore, andf embedded in aV body of silver within the lower portion of said' centerbore, said cylindrical flangeand-ring-tipportionsof the metal 'spindle being of piatinum and said shank; portion being a nickel wirev bonded to said cylindrical. portion.

6. A sparkfplug comprising'A ai generallytubularfmetal shell having at leastone platinum groundelectrode'wire secured tothe lowerend thereof, an elongated insulator having Ya centerbore therethrough andlsecuredconcentrically withinvsaid' shell, said'centerbore having', a lower portion of Vrediicedrdiameter,,anlupperA por'tion'offenlargedf-diameter and a shoulderbetween said upper and lower! portions, thefwall thickness of saidV insulator` diminishing.- gradually at the lowerendthereof adjacent'the groundwelectrodc; a: metal center electrode spindle havingle-platinum ringtip portion 'spaced' in sparkv gaprelation to said Vground electrode, a platinum ange portion abutting the lower end of said insulator and also spaced in spark gap relation to said ground electrode, a cylindrical portion litted snugly within the lower end of the insulator centerbore and a shank portion extending upwardly through the lower portion of said centerbore with a curved upper end in contact with said shoulder, said shank portion being embedded in a cast body of silver Within said centerbore, and a conductive glass seal in the upper enlarged portion of said centerbore bonded in electrical contact with said body of silver.

References Cited in the le of this patent UNITED STATES PATENTS Walsh Oct. 21,

Hensel Dec. 25,

Brinson May 23,

FOREIGN PATENTS France Sept. 19, 

